U.S. patent number 5,204,496 [Application Number 07/862,007] was granted by the patent office on 1993-04-20 for emi shielding gasket.
This patent grant is currently assigned to Digital Equipment Corporation. Invention is credited to Steven G. Boulay, Michael L. Joseph, Henry A. Rettstadt.
United States Patent |
5,204,496 |
Boulay , et al. |
April 20, 1993 |
EMI shielding gasket
Abstract
An EMI shielding gasket made of springy electrically conductive
material. The gasket includes a pair of generally parallel
laterally spaced apart U-shaped channel members each with its
channel entrance facing away from the other member. A pair of ends
oriented transversely of the U-shaped channel members connect the
members together at their end regions. The ends are resiliently
deformable to allow the U-shaped channel members to be moved more
closely together to facilitate mounting the gasket.
Inventors: |
Boulay; Steven G. (Schrewsbury,
MA), Joseph; Michael L. (Nashua, NH), Rettstadt; Henry
A. (Princeton, MA) |
Assignee: |
Digital Equipment Corporation
(Maynard, MA)
|
Family
ID: |
25337377 |
Appl.
No.: |
07/862,007 |
Filed: |
April 1, 1992 |
Current U.S.
Class: |
174/355;
361/818 |
Current CPC
Class: |
H05K
9/0016 (20130101) |
Current International
Class: |
H05K
9/00 (20060101); H05K 009/00 () |
Field of
Search: |
;174/35GC,35R,35MS,51
;361/424 ;219/1.55R,1.55D ;220/304,310 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Picard; Leo P.
Assistant Examiner: Ledynh; B. Lee
Attorney, Agent or Firm: Myrick; Ronald E. Young; Barry N.
Hudgens; Ronald C.
Claims
We claim:
1. An EMI shielding gasket for use at an opening in an enclosure
housing electronic components that radiate high frequency
electromagnetic emissions during operation comprising:
a pair of generally parallel laterally spaced apart U-shaped
channel members made of springy electrically conductive material,
each of the pair of U-shaped channel members including a
longitudinal bottom wall and two side walls extending from the
bottom wall in a direction generally opposite and away from the
other U-shaped member to terminate at a longitudinal channel
entrance opening facing away from the other U-shaped member, the
bottom and side walls being spaced and dimensioned to received in
mounting relationship an edge portion of the enclosure defining an
edge of the opening, a corresponding side wall each of the U-shaped
members comprising spaced apart wall segments, the free side of
each of such wall segments at the longitudinal channel entrance
having turned out corners each forming a resilient electrical
contact when the gasket is in EMI shielding use; and
a pair of parallel spaced apart springy electrically conductive
connecting portions oriented transversely of the U-shaped channel
members and joined thereto at their end regions, such connecting
portions being resiliently deformable to allow the U-shaped channel
members to be moved more closely together to facilitate mounting
the U-shaped channel members on opposite edges of the enclosure
opening.
2. The EMI shielding gasket of claim 1 wherein such gasket is made
of a single piece of metal.
3. The EMI shielding gasket of claim 1 wherein the corners of the
wall segments are turned outwardly from 20 to 30 degrees.
4. The EMI shielding gasket of claim 1 wherein the connecting
portions are planar and such planar connecting portions have a
mounting opening.
5. The EMI shielding gasket of claim 4 wherein the planar
connecting portions have tabs for placement of the gasket at an
enclosure opening.
6. An enclosure for housing electronic components that radiate high
frequency electromagnetic emissions during their operation
comprising:
a wall having an expansion opening;
An EMI shielding gasket mounted at the opening of the wall, the
shielding gasket having a pair of generally parallel laterally
spaced apart U-shaped channel members made of springy electrically
conductive material, each of the pair of U-shaped channel members
including a longitudinal bottom wall and two side walls extending
from the bottom wall in a direction generally opposite and away
from the other U-shaped member to terminate at a longitudinal
channel entrance opening facing away from the other U-shaped
member, the bottom and side walls being spaced and dimensioned to
receive in mounting relationship an edge portion of the enclosure
defining an edge of the opening, a corresponding side wall of each
of the pair of U-shaped members comprising spaced apart wall
segments, the free side opening having corners turned outwardly of
the channel, such turned out corners each forming a resilient
electrical contact when the gasket is in EMI shielding use; and a
pair of parallel spaced apart springy electrically conductive
connecting portions oriented transversely of the U-shaped channel
member and joined thereto at their end regions, such connecting
portions being resiliently deformable to allow the U-shaped channel
members to be moved more closely together to facilitate mounting
the U-shaped channel members o opposite edges of the enclosure
opening.
Description
BACKGROUND OF THE INVENTION
This invention relates to electromagnetic interference (EMI)
shielding, and more particularly to a gasket for shielding such
interference.
It is critical today to shield electronic equipment, such as
computers, against EMI emissions. In the past, computer products
worked with slower processors. Consequently, the problem of
escaping emissions of these types though openings in computer
enclosures was not significant. But the advent of faster processors
and switching has changed this. While increased processing speeds
have made remarkable improvements in computer performance and
efficiency, EMI containment problems have been exacerbated.
Today it is not uncommon for computers to use clock speeds in the
range of 50 to 200 MHz or more. And digital circuits operating at
these high frequencies may have pulse rise times of a nanosecond or
less. These speeds can cause EMI to be radiated at harmonic
frequencies in excess of 1 GHz.
The Federal Communications Commission (FCC) has established
standards that limit the amount of allowable EMI emissions from
electronic devices. To meet FCC emissions standards it is necessary
to seal around slots holding expansion or option cards and to seal
around slots covered by blanks when these slots are not being used.
This task is challenging in today's commercial environment.
Then too, there is commercial pressure to compact the spacing
between expansion slots or openings, while still providing standard
EISA/ISA expansion slots or openings. These standard slot sizes are
needed to maintain interchangeability of expansion or option cards
between computers even as market forces press to reduce the size of
computers. This need has not been effectively met.
In the past one approach to sealing around slots and openings has
been the use of individual shielding strips or clips to inhibit EMI
emissions though such openings in enclosures containing electronic
equipment giving off such emissions during its operations. U.S.
Pat. No. 5,029,254 discloses an example of a shielding strip, which
is held in place at the edge of an opening by a clamping element.
During mounting of expansion or option cards, shielding strips and
clips are easily knocked off. Mounting is difficult at best.
U.S. Pat. No. 4,659,869 discloses another example of a clip-on
shielding strip. Shielding strips like those disclosed in these two
examples present considerable difficulty. They are individually
placed in position on the edges of enclosures and have the same
difficultly as those mentioned in connection with the shielding
strips disclosed U.S. Pat. No. 5,029,254.
Accordingly, there still exits a need for a shielding arrangement
that is easily installed and that effectively retards EMI
emissions.
SUMMARY OF THE INVENTION
The EMI shielding device of the invention is a gasket that is
easily mounted on enclosure edge regions defining an opening
requiring EMI shielding and that is self-aligning.
In a broad sense, the invention is a EMI shielding gasket made of
springy electrical conducting material that includes pair of spaced
apart channel members comprising resilient electrical contact means
and a pair spaced apart connecting portions joining the two channel
members together.
In a more specific sense, the gasket of the invention includes a
pair of laterally spaced apart U-shaped channel members made of
springy electrically conductive material joined together by a pair
of spaced apart connecting portions also made of springy
electrically conductive material. The connecting portions are
oriented transversely of the U-shaped channel members and joined
thereto at the end regions of the channel members. Further, the
connecting portions are resiliently deformable to allow the
U-shaped channel members to be moved more closely together to
facilitate mounting.
The U-shaped channel members each includes a longitudinal bottom
wall and two laterally spaced sidewalls extending from the bottom
wall in a direction generally opposite and away form the other
U-shaped member. These two sidewalls terminate at their free sides
at a longitudinal channel entrance opening facing away from the
other U-shaped member. Moreover, the walls of the U-shaped channel
members are spaced and dimensioned to receive in mounting
relationship an edge portion of the enclosure defining a slot or
opening to be shielded. Further, a corresponding sidewall of each
of the U-shaped members comprises spaced apart wall segments. And
these segments have corners at their termination or free side that
are turned outwardly of the channel. These turned out corners
function as resilient electrical contacts when the gasket is in EMI
shielding use.
The gaskets as disclosed herein allow more closely spaced expansion
slots, including standard slots, and does so while providing good
electrical contact with circuit cards, slot covers, and the like to
effect EMI shielding.
Other objects, features, and advantages of the invention will
became apparent as the invention is described in more detail with
reference made to the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of a portion of a computer using EMI
shielding gaskets according to the principles of the invention in
connection with vertically oriented expansion slots.
FIG. 2 is an enlarged isometric view of a interior expansion slot
region of the computer shown in FIG. 1.
FIG. 3 is a somewhat enlarged isometric view of the EMI shielding
gasket shown in use in FIGS. 1 and 2.
FIG. 4 is a side elevation view of the EMI shielding gasket of FIG.
3.
FIG. 5 is a plan view of the EMI shielding gasket of FIG. 4.
FIG. 6 is a section view of an the EMI gasket and expansion slot
shown in FIGS. 1-5 with the gasket held in a bowed condition in
preparation for mounting in the expansion slot.
FIG. 7 is a section view of the EMI gasket of FIG. 6 mounted at the
expansion slot.
FIG. 8 is a isometric view of an alternate EMI shielding
gasket.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a computer 10 that includes a metal enclosure 12 that
comprises a top wall 14, a sidewall 16, and a base 18. As shown,
the sidewall 16 has three vertically aligned rectangularly shaped
expansion slots 20. The enclosure 12 holds computer components,
such as storage cards 21, and electronic components (not shown)
that emit high frequency EMI.
Mounted on the enclosure 12 at each of the expansion slots 20 is an
EMI shielding gasket 22 made of thin springy electrically
conductive material, such as stainless steel or beryllium copper.
As can be more clearly seen in FIGS. 2-4, the shielding gaskets 22
as shown are rectangularly shaped to conform to the slots 20 and
are formed by spaced apart U-shaped channel side members 24 and
transversely oriented ends 26.
Each of the U-shaped channel side members 24 includes a
longitudinal bottom wall 28 and latterly space apart sidewalls 30
and 32 that extend in laterally spaced apart relationship from the
bottom wall 28 in a direction opposite and away from the other
U-shaped channel side member 24 to define a mounting channel 33.
The sidewalls terminate at an entrance 34 to the channel 33.
The ends 26 are thin planar portions that are resiliently
deformable and that have mounting openings 36 and tabs 37. The tabs
37 are for use with stop recesses or the like, such as indent 39
(FIG. 2), on the inside surface of an enclosure to assist in
keeping a gasket 22 in place. As shown, each of the gaskets 22 is
made of a single thin piece of metal, such as stainless steel or
beryllium copper. The sidewalls 32 of each of the gaskets 22 lie in
the same plane as the planar end portions 26. Accordingly, when
mounted, the sidewalls 32 and the end portions 26 are at the inside
surface of an enclosure. The sidewall 30 of each of the gaskets 22
lies in a plane latterly offset by the width of the bottom wall 28,
and consequently, is on the outside of an enclosure when a gasket
22 is mounted.
As shown, each of the sidewalls 32 is formed of individual wall
segments 38, which are separated by narrow spaces or slots 40. And,
as indicated, the segments 38 lie in the same plane as the planar
end portions 26 and include corners 42 turned outwardly of the
channel 33. As shown, slots, denoted by reference numeral 40a, that
are the same size and spacing as slots 40 continue into ends 26.
And at these slots 40a there are turned out corners, denoted by
reference numeral 42a, that are the same size and shape as turned
out corners 42. These turned out corners 42 and 42a function as
electrical contacts when a gasket 22 is in EMI shielding use.
Because the gaskets 22 are made of springy material such as
stainless steel, the turned out corners 42 and 42a themselves are
resilient or springy. Accordingly, the corners 42 and 42a provide
good pressing of resilient electrical contact with an expansion
card face plate, cover, or the like that is fixed in place over an
opening or slot of an enclosure at which a gasket 22 is used.
In practice, the distance between slots 40 will vary. Accordingly,
the space between the turned out corners 42 and 42a will vary, in a
conventional way, depending upon the frequency of EMI emitted by
electronic components held in an enclosure to effect good EMI
shielding.
FIG. 2 shows a view of the interior expansion slot region of the
computer enclosure 12 with an option or expansion card 44 in place
at one of the expansion slots 20. The card 44 includes a circuit
card 46 and a connector or face plate 48. Screws 50 fix the card 44
to the interior surface of the sidewall 16. And there is a gasket
22 mounted at the slot 20 that is covered by the face plate 48 of
the card 44. The turned out corners 42 and 42a of that gasket 22
are pressed by the contacting surface of the face plate 48. So the
corners 42 and 42a are resiliently urged into electrical contact
with the face plate 48.
FIG. 6 shows one of the gaskets 22 held in position to be mounted
at a slot 20. As indicated, the ends 26 are held in a bowed
condition for snap-in mounting of the gasket 22. In this bowed
condition the U-shaped side channel members 24 of the gasket 22 are
placed closer together for ease of mounting and the channel
entrances 34 are disposed for easier mounting. FIG. 7 shows the
gasket 22 mounted at the slot 20 with a slot cover 54 positioned to
cover the slot 20. When mounted, the ends 26, which are resiliently
deformable, are once again planar and the edge regions 52 of the
enclosure 12 defining the slot 20 have been received in mounted
relationship in the channels 33 of the U-shaped members 24.
Shielding gaskets like those shown in FIGS. 1-6 can be used to
provide effective EMI shielding for enclosures containing
electronic components generating emissions over a range of
frequencies. As shown, the gasket 22 is aimed at shielding
frequencies up and including a range of from about 1 to 10 GHz. For
this range, and referring to FIG. 5, a gasket 22 has been used that
has a length, l, of 4.38 inches and a width, W, of 0.980 inches.
The height, h, of the sidewalls 30 and 32 is 0.127 inches, and the
length, l, of the segments 38 is 0.450 inches. The width of the
slots 40 is 0.05 inches. The corners 42 and 42a are turned
outwardly an angle A (FIG. 4) of from 20 to 30 degrees, 25 degrees
being usual. The gaskets 22 are normally made from zero gauge
stainless steel having a thinness of 0.003-0.004 inches.
FIG. 8 is a view of an alternate embodiment of the invention. In
FIG. 8 there is shown a shielding gasket 122 made of thin springy
electrically conductive material, such as stainless steel or
beryllium copper. The gasket 122 is defined by spaced apart
U-shaped side members 124 and transversely oriented ends 126.
Each of the U-shaped side members 124 includes a bottom wall 128
and two latterly spaced apart sidewalls 130 and 132 that extend
from the bottom wall 128 in a direction opposite and away from the
other U-shaped side member 124 to define a mounting channel 133.
The sidewalls 130 and 132 terminate at an entrance 134 to the
channel 133. And the sidewall 132 has a spring or resilient
electrical contact portion 135 running the length of the sidewall
132. As shown, the contact portion 135 has been formed by being
bend at the free side of the sidewall 132. The portion 135 is
inclined to the plane of the gasket 122 at an angle of from about
20-30 degrees, normally 25 degrees. The contact portion 135 and the
sidewall 132 are connected by spaced apart connectors 138. These
connectors 138 function to allow the surface of the contact portion
135 conform to any non-uniformities in a contacting surface.
In practice, the electric contact portions 135 make resilient or
springy electrical contact with a metal enclosure when place in EMI
shielding at an opening or slot of an enclosure.
The ends 126 are thin planar portions that are resiliently
deformable and that have mounting openings 136. And, as shown, the
gasket 122 is made of a single thin piece of metal, such as
stainless steel or beryllium copper. The sidewalls 130 and 132 lie
in the same plan as the end 126.
Like the shielding gasket shown in FIGS. 1-7, gasket 122 can be
used with enclosures containing electronic components generating
emissions over a range of frequencies. As shown, the gasket 122 is
aimed at shielding frequencies up to and including a range of about
1 to 10 GH.sub.z. As shown in FIG. 8, the connectors 138 are spaced
apart a distance, d, of 0.135 inches and have a width, w, of 0.06
inches. The height, h, of the sidewall 132 is 0.130 inches.
It will be appreciated that the gaskets 22 and 122 have been
depicted for use at a standard EISA/ISA opening or slot. Hence, it
is to be understood that gaskets according to the principles of the
invention can be other shapes and sizes.
It is apparent that within the scope of the invention modifications
and different arrangements may be made other than herein disclosed
other than herein disclosed. The disclosure is merely illustrative,
the invention comprehending all variations thereof.
* * * * *